First broken bit!

[supertigre]

Over tightening the collet will also cause it to break where it did.

[coryatjohn]

Guy,

I just put enough oomph into the collet as it needs to stay where it needs to be. TJ at the ShopBot class in Durham was pretty clear on what tension is needed. I think that class was quite useful.

[curtiss]

Have not seen Brady help out on this thread.

I guess he has never broken one...

What is the most expensive bit anyone has broken / or even purchased ?

[Brady Watson]

Have not seen Brady help out on this thread.

I guess he has never broken one...

What is the most expensive bit anyone has broken / or even purchased ?

Nope. Never. Not even once.

I'm Scotch. It is against the rules

Y'all are doing just fine without my input...carry on

-B

[dana_swift]

@John: Unlike Brady, I have broken many bits. I suspect I will break more in the future. I guess he can deduce the optimum feeds, speeds, and bit mounting for any application and material. I on the other hand, have to break bits to learn!

About the only thing I can do with guaranteed accuracy is predict when the collet will collide with the stock, meaning the bit needs to protrude a little more. After that, I have found "safe zones" for feeds and speeds, but nothing is guaranteed. Any defect in the carbide, dirt between the bit and the collet start the process of crack propagation in the bit shank.

Heat is a huge culprit in eating bits. Keep the feed rates in the sweet spot where the chip load calculations say it should be and that is the best place to start. Then the unknown is what should the pass depth be? No equations to help us there. Just experience. Shallow cuts at the correct feed rate are easiest on the bit. Deep cuts get the job done sooner "sometimes". Sometimes we find ourselves mid-cut having to hit the space bar and change to a new bit.

The depth of cut is determined by the horse power available to push the cutting edge of the bit through the material, as well as the flex resistance of the bit. If the bit is thin, that becomes the limiting factor. If its a half inch bit with lots of meat, the horsepower is the limiting factor on the cut depth.

Its always safe to go shallow, but its not safe to go slow. A year or two from now you will find there is a good sized sweet spot you can go to with little fear of replacing bits too soon. If the chip load calculation shows a feed rate of "X", you will probably be just fine with "X-1" or "X+1". (Did you know you can change the feed rate while the bot is cutting?) Experiment.

Also one last note- I keep several spares of my most used bit sizes. Sometimes I change a broken bit and "fix the problem" to discover it was a different problem breaking the bits.

Also- NEVER drop a carbide bit on a hard surface. That starts cracks in it and it is just a short time till it breaks under load. Shattering is a possibility. You do wear safety glasses don't you?

I'm sure Brady has never had a bit shatter either! But since he is one smart cookie, I bet he wears safety glasses (just in case of a manufacturing defect I suppose)..

D

[Brady Watson]

Don't be fooled...I got a whole bin full of broken bits ...I'm not sure exactly why I haven't just thrown them out. Maybe I am thinking they could be used for something else. I have taken a few of them and sharpened them to a point and used it as a precise indicator for setups etc.

If you run a job shop and get into some of the more exotic materials, you are going to break some bits trying to find that chipload sweet spot. Generally speaking, I care little about chipload. I am focused on cut quality first, then if I can eek out a few more parts by dialing down RPM/rubs then great. The problem with using chipload calculators is that there is zero consideration for how the part are held down - that is to say, that it assumes that the geometry of the tool and your hold down solution are not fighting each other to the point that it will cause the parts to lift or move. Sometimes you have NO other choice than to grossly lighten up chipload in order to keep the part from breaking free from the hold down...so you kill a tool or two...You get the job done, and you get paid.

So...I don't want to invalidate the science of chipload, because it IS 100% valid from an engineering point of view. I'd love for tools to last a lot longer because I was able to run at ideal settings. BUT, the hard truth is, with our machines, running ideal chipload doesn't really happen as often as you'd think - and there are even more variables that you have to consider, such as the shape of each part & whether you are going to defy the laws of physics with acceleration and deceleration on parts that have convoluted curves. Large parts, like those for cabinets etc, are much easier to dial in than say, a bunch of smaller 'amoeba' shaped parts. So keep that in mind.

If you get in the 'ballpark' with chipload settings, then you're golden...and just to dispel some of the mystique behind chipload, if you let the router rooster-tail some chips into your cupped hand, and you mic out the thickness of the chip, that's you're chipload. Nothing more than that.

Truth be told - No. I don't always wear glasses. If I am just cutting sheet goods and lumber, no. If I am hammering @ 12" per second with chips flying everywhere - with so many matchsticks you can't even use dust collection - then yes. If I am cutting any kind of HDU, metal or aramid/graphite - yes. Static electricity is a strange thing...move your part with the machine off & static charges can propel chips in your face. Ask me how I know!

-B

[gerryv]

According to the Clan Watson Society of Canada, the Lord Lyon has confirmed that the clan does have a chief, but the title has not been claimed since it was held by James Watson of Saughton in 1818.

Hey maybe we could start a movement to have Brady named chief and he could invite us to his Scottish castle.

[FSICM]

pull your collar off and blow it out make sure there is no dirt or dust in it
I broke 2 back to back because the collar didn't tighten properly.

[chiloquinruss]

I get asked often how I learned to run a cnc machine, and I reply 'experience', then I go over to my toolbox and get the bag of 'experience' to show them the broken bits. Most of them are becuase of cockpit error and not a faulty part or setting, just DUMB stuff! Russ

[beacon14]

Save up your broken and dull bits and send them in for ca$h:

http://ibuyscrapcarbide.com/

I haven't tried it yet but I found this guy at the IWF and plan to give it a go. I probably have a couple hundred bucks worth of used carbide in the jar - I knew there was a reason to not throw them out.